Boron trifluoride or a boron trifluoride complex consisting of boron trifluoride and a complexing agent (ligand) is well known as a so-called Friedel-Crafts catalyst and has excellent catalyst performance of suppressing side reactions and promoting only main reactions effectively as compared with AlCl3, FeCl3, sulfuric acid and the like. Therefore, boron trifluoride and its various complexes are industrially used widely as a catalyst in various chemical reactions such as alkylation, isomerization, polymerization, dimerization, condensation, addition, decomposition, dehydration, etc.
Main industrial use of boron trifluoride includes a catalyst in manufacturing ethylbenzene by gas phase alkylation from ethylene and benzene. Alkylbenzenes used for synthetic detergents or anti-oxidants are manufactured by liquid phase alkylation reaction of olefins and aromatics, where boron trifluoride or its complexes is also used as the catalyst in the manufacture.
Furthermore, boron trifluoride or its complexes is also used as a polymerization catalyst in manufacturing petroleum resins and chromane-indene resins, which are widely used in the fields such as adhesives and printing ink, and when this catalyst is used, it has the effect that there is less deterioration of a product and corrosion of equipment. As mentioned above, boron trifluoride or its complexes is a catalyst provided for various uses as a manufacturing catalyst in chemical industry.
A catalyst comprising boron trifluoride or a boron trifluoride complex consisting of boron trifluoride and a complexing agent is used, depending on the reaction of interest, in the form of boron trifluoride alone or a complex in which various compounds are coordinated to boron trifluoride at an appropriate ratio. It is general that boron trifluoride is deactivated to separate a reaction product and a catalyst after completion of the reaction in which boron trifluoride or its catalyst is used. For separation of the reaction product and the catalyst, a process of washing the reaction product by adding water to the reaction solution to deactivate boron trifluoride and a process of washing the reaction product after neutralizing the reaction solution by basic aqueous solutions such as ammonia, sodium hydroxide, and lime are usually adopted.
However, since the waste water containing fluorides or boron, composed of a hydrate of boron trifluoride or a neutralized product of boron trifluoride in high concentrations, is discharged in the washing process or the neutralizing process, it is recently desired to take measures for removal of the waste water containing fluorides or boron in consideration of the problem of environmental pollution. In particular, since it is difficult by the present technology for waste-water treatment to remove boron easily, and since it is costly to remove boron completely, it is desired to remove boron at a low cost. Furthermore, since boron trifluoride is expensive, it is expected to recover and reuse the removed boron trifluoride.
In the condensation reaction of olefin using boron trifluoride or boron trifluoride complexes as a catalyst, even if the reaction product solution is allowed to stand, the boron trifluoride complex is almost dissolved in the reaction product or forms an emulsion, and hence it is difficult to completely separate the reaction product and the boron trifluoride complex catalyst. Therefore, boron trifluoride is removed from the reaction product by washing with water or a basic aqueous solution. However, if water or the basic solution is added to the boron trifluoride complex, the boron trifluoride catalyst forms a water complex such as BF3.(H2O)n or a boron trifluoride salt, and cannot be repeatedly used as a catalyst without change. Although a process of separating the catalyst layer and the reaction product using a complex of BF3 with phosphoric acid, acetic acid or phenol is also disclosed (for example, refer to Japanese Patent Application Laid-open No. Heisei02(1990)-45429 (p1–6)), the reaction proceeds only slowly unless the catalyst concentration is 10% or more. Moreover, separation of the reaction product and the catalyst is inadequate and the amount of the catalyst that can be reused is limited. Moreover, since the catalyst acts as a Broensted acid, side reactions such as isomerization occur, and consequently the aforementioned process of separation cannot be adopted particularly for the condensation dimerization reaction of olefin.
Conventionally, there is disclosed a process for the recovery of boron trifluoride, wherein the reaction product solution containing boron trifluoride or a boron trifluoride complex is contacted with calcium fluoride (CaF2) at the temperature of 200° C. or less, the generated calcium tetrafluoroborate (Ca(BF4)2) is heated at the temperature between 100 and 600° C., and boron trifluoride is recovered by obtaining boron trifluoride and calcium fluoride (for example, refer to Japanese Patent Application Laid-open No. 2000-109313 (p1–9)).
Similarly, there is disclosed a process for the recovery of boron trifluoride by generating tetrafluoroborate using a fluoride such as lithium fluoride, strontium fluoride, and barium fluoride and heating at the temperature between 100 and 600° C. (for example, refer to Japanese Patent Application Laid-open No. 2000-128522 (p1–9), Japanese Patent Application Laid-open No. 2000-135402 (p1–9), and Japanese Patent Application Laid-open No. 2000-135403 (p1–9)).
However, in the reaction using boron trifluoride as a catalyst, it is necessary to react at low temperature below room temperature in many cases. Moreover, when the temperature is raised to around 100° C. after completion of the reaction, at which tetrafluoroborate is synthesized advantageously, a side reaction occurs and causes decrease in the yield or lowering of the quality of a reaction product of interest. The complex is hardly formed below room temperature. Moreover, decomposition reaction by heating at high temperature is not desirable from a viewpoint of energy saving.
Moreover, there is a problem that, when the reaction product solution is viscous, it is difficult to separate the reaction product completely from borates such as calcium tetrafluoroborate, which takes time and effort.
A process for the recovery of boron trifluoride complexes is also disclosed, wherein the boron trifluoride complex is precipitated and separated from a nonconducting fluid by applying direct current and/or alternating voltage to the nonconducting fluid in which boron trifluoride is dispersed and/or dissolved and subsequent warming of the separated complex (for example, refer to Japanese unexamined patent publication (Kokai) No. 2001-104805 (p1–11)).
However, in this process for the recovery, it is necessary to continue to apply a voltage of several hundreds of volts from an external power supply for 30 minutes or more after completion of the reaction. Since the reaction proceeds further and a side reaction occurs if the voltage supply is continued, a process for stopping the reaction is required. There is also a problem that the boron trifluoride complex dissolved in the reaction mixture is not always separated. In addition, it was necessary to provide an electric equipment system, and it was difficult to completely separate the boron trifluoride complex by this recovery process.